Electromagnetic device



May 21, 1968 c. WEATHERS ELECTROMAGNETIC DEVICE Filed June 27, 1966 lawminm 213 2 wmemok ARMATURE ANGLE DEG.

United States Patent 3,384,848 ELECTROMAGNETIC DEVICE Leland Clay Weathers, Plymouth, Mich, assignor to Sperry Rand Corporation, New York, N.Y., a corporation of Delaware Filed June 27, 1966, Ser. No. 560,628 14 Claims. (Cl. 335-268) ABSTRACT OF THE DISCLOSURE A solenoid has a stator, has two selectively-energizable windings on that stator, has an armature that is movable in one direction by one of those windings and that is movable in the opposite direction by the other of those windings, has a generally linear magnetic gap adjacent one end of one side of that armature and an inverse magnetic gap adjacent the other end of that side of that armature, has a second generally linear magnetic gap adjacent one end of the other side of that armature and an inverse magnetic gap adjacent the other end of that other side of that armature, and has a spring that normally centers that armature between those generally linear gaps.

This invention relates to improvements in electromagnetic devices. More particularly, this invention relates to improvements in solenoids.

It is, therefore, an object of the present invention to provide an improved solenoid.

Customarily, the armatures of solenoids are initially spaced short distances away from the pole pieces of those solenoids; and the windings of those solenoids must be energized to move those armatures toward those pole pieces. When those armatures are in their initial positions, the effective values of the pulls which the magnetic flux lines from the windings apply to those armatures are small; but those values increase materially as those armatures approach the pole pieces of those solenoids. Frequently, the armatures apply hammenlike blows to the pole pieces of the solenoids as they move into engagement with those pole pieces. It would be desirable to provide a solenoid which required a smaller-than-usual magnetizing force to move the armature thereof and which applied smaller-than-usual forces to that armature as the armature approached the pole piece thereof. The present invention provides such a solenoid; and it does so by equipping that solenoid with the combination of an inverse magnetic gap and a generally linear magnetic gap of progressively-smaller width.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and acompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. 1 is an elevational view of one preferred embodiment of solenoid that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is a sectional view through the solenoid of FIG. 1, and it is taken along the plane indicated by the line 2-2 in FIG. 1.

FIG. 3 is a sectional view on a larger scale through the solenoid of FIG. 1, and it is taken along the plane indicated by the line 33 in FIG. 2,

FIG. 4 is a sectional view, on a slightly larger scale, of a portion of the structure shown in FIG. 3, and it ice shows one of the moved positions of the armature by dotted lines, and

FIG. 5 is a graph showing torque-displacement curves plus the trace of the current flowing through the solenoid shown in FIG. 1.

Referring to the drawing in detail, the numeral 20 denotes a generally U-shaped plate which is mounted at the front of the solenoid shown in FIG. 1; and a similar U-shaped plate 22 is disposed at the rear of that solenoid. A number of generally U-shaped laminations 23 are held in assembled relation with each other and with the generally U-shaped plates 20 and 22 by fasteners 25 and 35, such as spring pins and shouldered screws, respectively. The free ends of the arms of the generally U-shaped laminations 23 are fixed, secured to each other by fasteners, such as rivets 27, which are shown particularly by FIG. 3. Further generally U-shaped laminations 24 are held in assembled relation with each other and with the generally U-shaped plates 20 and 22 by fasteners 26 and 37, such as spring pins and shouldered screws, respectively. The free ends of the arms of the generally U-shaped laminations 24 are fixedly secured to each other by fasteners 29, such as rivets, which are shown particularly by FIG. 3. The assembled laminations 23 and 24 are disposed so the free ends of the upper arms thereof are in register with each other and so the free ends of the lower arms thereof are in register with each other, as shown particularly by FIG. 3.

The free ends of the upper arms of the U-shaped laminations 23 have surfaces 28 and 30 thereon which coact to subtend an obtuse angle that is close to ninety degrees. The free ends of the lower arms of the U-shaped laminations 23 define a surface 32 which is inclined to the axes of those lower arms and which is co-planar with the surface 30. The free ends of the upper arms of the generally U-shaped laminations 24 have surfaces 34 and 36 thereon which coact to subtend an obtuse angle that is close to ninety degrees. The free ends of the lower arms of the generally U-shaped laminations 24 define a surface 38 which is inclined to the axes of those lower arms and which is co-planar with the surface 36. The plane defined by the surfaces 36 and 38 on the free ends of the arms of the U-shape laminations 24 is inclined to the plane defined by the surfaces 30 and 32 on the free ends of the arms of the U-shaped laminations 23; and those planes subtend an angle of about twenty degrees. The U-shaped laminations 23 and the U-shaped laminations 24 constitute the stator of the solenoid; and that stator is generally denoted by the numeral 39.

The numeral 40 denotes a coil form which supports a coil 42; and that coil form is telescoped over the upper arms of the U-shaped laminations 23. The numeral 44 denotes a coil form which supports a coil 46; and that coil form is telescoped over the upper arms of the U-shaped laminations 24. The coil forms 40 and 44 will fit snugly on the upper arms of the U-shaped laminations 23 and 24, respectively. The coils 42 and 46 are selectively connectable to a source of power by switches or contacts, not shown.

The numeral 50 denotes plates which are generally rectangular in elevation, and those plates have notches 57 in the lower ends thereof. Those plates are disposed at the front and rear faces of a number of generally rectangular armature laminations 52. Fasteners 54, such as rivets, fixedly secure the laminations 52 to each other and to the plates 50. The plates 50 and the armature laminations 52 have aligned notches therein; and those aligned notches accommodate shading rings 55. Those shading rings can be of standard and usual design and construction. The plates 50 and the armature laminations 52 constitute the armature of the solenoid; and that armature is generally denoted by the numeral 53. The upper ends of the armature laminations 52 are arcuate, and those upper ends are concentric with the shaft 56. The portions of the armature laminations 52, that are intermediate the shading rings 55, project laterally beyond the edges of those laminations to provide bearing surfaces 49 and 51.

The numeral 58 denotes bushings which are mounted Within aligned openings in the plates 20 and 22; and those bushings are coaxial. The shaft 56 is loosely supported by those bushings; and that shaft extends through and is fixedly secured to the plates 50 and to the armature laminations 52. Srping retainers 60, in the form of shouldered sleeves, are telescoped over the outer ends of the shaft 56; and fasteners 61, such as C-washers, are seated within grooves in the shaft 56 adjacent the outer faces of the spring retainers 60. Those C-washers and the spring retainers 60 coact with the plates 20 and 22 to hold the armature 53 of the solenoid against axial movement relative to the stator 39 of that solenoid.

The numeral 62 denotes wire-like springs which are Wound around the spring retainers 60; and the free ends of those springs abut pins 66 and 68 that project outward- 1y from the front and rear faces of the armature 53 to force the springs 62 to assume the configuration shown by FIG. 1. The springs 62 are stressed as they are moved into position to engage the pins 66 and 68; and the restorative forces within those springs will urge the portion of the spring 62, shown in FIG. 1, which inclines upwardly from lower right to upper left against the left-hand face of the pin 68, and will force the portion of that spring which extends from lower left to upper right against the righthand face of the pin 66. The confronting faces of the upwardly-extending portions of the springs 62 bear against the projecting ends of the pin 64 which is carried by the armature 53, and which extends forwardly and rearwardly, respectively, from the front and rear faces of that armature. The springs 62 tend to hold the armature 53 in the position shown by FIGS. 1 and 3 and shown in solid lines by FIG. 4. In that position, that armature is approximately mid-way between the moved position shown by dotted lines in FIG. 4 and by the other moved position of that armature.

The notches 57 in the lower ends of the plates 50 of the armature 53 accommodate a pin 70; and that pin serves as an actuator for the device which is to be actuated by the solenoid. That actuator is located close enough to the axis of the shaft 56 to provide substantially linear movement for the actuated portion of the device which is actuated by the solenoid.

The surface 28 on the free ends of the upper arms of the U-shaped laminations 23 is tangential to an are that could be scribed with the axis of the shaft 56 as the center thereof and with the upper end of the surface 30 as a starting point. The surface 34 on the free ends of the upper arms of the U-shaped laminations 24 also is tangential to that arc. As a result, those surfaces can coact with the upper end of the armature 53 to define generally linear magnetic gaps of progressively decreasing width.

Whenever the coil 42 is energized, magnetic flux lines will flow through the upper arms of the generally U- shaped laminations 23, through the closed ends of those laminations, through the lower arms of those laminations, across the inverse magnetic gap between the surface 32 and the armature 53, through that armature, and then across the magnetic gaps between that armature and the surfaces 28 and 30. The armature 53 will respond to those magnetic flux lines to rotate in the counterclockwise direction until the bearing surfaces 49 and 51 at the lefthand face of that armature abut the surfaces 30 and 32. At the instant the coil 42 is energized, the density of the magnetic flux lines at the magnetic gap between the surface 32 and the armature 53 will be greatest adjacent the lower portion of that surface. Also, the density of the magnetic flux lines at the magnetic gaps between the armature 53 and the surfaces 28 and 30 will be greatest adjacent the upper portion of the surface 28. As the armature 53 responds to the magnetic flux lines from the coil 42 to rotate in the counter clockwise direction in FIGS. 1 and 3, the distribution of the magnetic flux lines will change; and the density of those magnetic flux lines will progressively increase upwardly along the length of the surface 32. Also as the armature moves in the counter clockwise direction, the density of the magnetic flux lines will progressively increase along the lower portion of the surface 28 and along the surface 30. Because the upper portion of the surface 28 is closely adjacent the upper end of the armature 53, at the instant the coil is energized, a larger-than-normal force will be applied to that armature at the instant that coil is energized. This is very desirable, because it assures prompt initiation of the movement of the armature 53.

As the left-hand face of the armature 53 approaches the surfaces 30 and 32 on the upper and lower arms, respectively, of the generally U-shaped laminations 23, the pull which the magnetic flux lines passing through those surfaces apply to that armature will increase. However, the forces which the flux lines passing through the surface 28 apply to the armature 53 also will increase. As a result, the torque-displacement curve of the solenoid shown in FIG. 1 tends to be flatter than the torque-displacement curve of a similar solenoid which has an arcuate surface rather than the tangential surface 28.

Referring to FIG. 5, the numeral 74 denotes the torquedisplacement curve which is due solely to the magnetic flux lines at the magnetic gap between the surface 32 and the armature 53. The numeral 76 denotes the torque-displacement curve which is due solely to the magnetic flux lines between the surfaces 28 and 30 and the armature 53. The numeral 78 denotes the torque-displacement curve which is due to the magnetic flux lines at the magnetic gap between the surface 32 and the armature 53 plus the magnetic flux lines between the surfaces 28 and 30 and that armature. The curve 78 is substantially flat throughout more than three-quarters of the displacement of the armature from zero degrees to ten degrees. This is a very desirable torque-displacement curve; and it provides a higherthan-normal pull on the armature when that armature is displaced from the stator 39 and provides a lower-thannormal pull on that armature when that armature is closely adjacent that stator.

The numeral 88 denotes the torque-displacement curve of the solenoid whenever the coil 42 is receiving only eighty-five percent of its normal current. That curve also is generally fiat throughout more than three-quarters of the displacement of the armature between zero degrees and ten degrees; and this is important because it makes certain that the torque developed throughout that entire curve is greater than the returning torque provided by the springs 62. The curve 72 shows how the current through the coil 42 increases as that coil is energized-that current falling from about two and one-tenth root mean square amperes to a very low value as the armature 53 moves from the position shown by FIGS. 1 and 3 to one of its moved positions.

Whenever the coil 42 is de-energized, the springs 62 will return the armature 53 to the mid-position shown by FIGS. 1 and 3. The holding value of the residual magnetism within the generally U-shaped laminations 23 will be reduced by the inconstant width of the magnetic air gap between the surface 28 and the arcuate upper surface of the armature 53. This is desirable, because it permits prompt and immediate return of the armature 53 to its normal position.

Whenever the coil 46 is energized, magnetic flux lines from that coil will flow through the upper arms of the generally U-shaped laminations 24, through the closed ends of those laminations, through the lower arms of those laminations, across the inverse magnetic gap between the surface 38 and the armature 53, through that armature, and then across the magnetic gaps between that armature and the surfaces 34 and 36. The armature 53 will respond to those magnetic flux lines to rotate in the clockwise direction until the bearing surfaces 49 and 51 at the right-hand face of that armature abut the surfaces 36 and 38. At the instant the coil 46 is energized, the density of the magnetic flux lines at the magnetic gap between the surface 38 and the armature 53 will be greatest adjacent the lower portion of that surface. Also, the density of the magnetic flux lines at the magnetic gaps between the armature 53 and the surfaces 34 and 36 will be greatest adjacent the upper portion of the surface 34. As the armature 53 responds to the magnetic flux lines from the coil 46 to rotate in the clockwise direction in FIGS. 1 and 3,. the distribution of the magnetic flux lines will change; and the density of those magnetic flux lines will progressively increase upwardly along the length of the surface 38. Also as that armature moves in the clockwise direction, the density of the magnetic flux lines will progressively increase along the lower portion of the surface 34 and along the surface 36. Because the upper portion of the surface 34 is closely adjacent the upper end of the armature 53, at the instant the coil 46 is energized, a larger-than-normal force will be applied to that armature at the instant that coil is energized. This is very desirable, because it assures prompt initiation of the movement of the armature 53.

As the right-hand face of the armature 53 approaches the surfaces 36 and 38 on the upper and lower arms, respectively, of the generally U-shaped laminations 24, the pull which the magnetic flux lines passing through those surfaces apply to that armature will increase. However, the forces which the flux lines passing through the surface 34 apply to the armature 53 also will increase. As a result, the torque-displacement curve 78 of FIG. 5 also will apply when the coil 46 is energized.

Whenever the coil 46 is de-energized, the springs 62 will return the armature 53 to the mid-position shown by FIGS. 1 and 3. The holding value of the residual magnetism within the generally U-shaped laminations 24 will be reduced by the inconstant width of the magnetic air gap between the surface 34 and the arcuate upper surface of the armature 53. This is desirable, because it permits prompt and immediate return of the armature 53 to its normal position.

It will be noted that the springs 62 are supported by the spring retainers 60 and act directly upon the pin 64 which is carried by the armature 53 of that solenoid. This is desirable, because it relieves the actuated device from the pressures that are provided by the springs 62. This also is desirable, because it enables the shaft 56 and the armature 53 to rotate relative to. the loops defined by the springs 62 while permitting the ends of those springs to act upon the pin 64 carried by that armature.

It also will be noted that the pin 64 is located at the approximate center of the forces applied to the armature 53. Furthermore, it will be noted that the actuator 70 is spaced from, and does not directly contact, any of the armature laminations 52. The overall result is that the armature laminations 52 are not subjected to external loading, and the only impact which must be withstood by those armature laminations is that between the armature 53 and the laminations 23 and 24 of the stator 39.

The solenoid provided by the present invention can move the armature thereof between its normal position and either of its moved positions within the span of one cycle of sixty cycle alternating current. During the first three-quarters of the movement of that armature, the force applied to that armature will be generally constant; and it will be higher than the force which a standard inverse-gap solenoid will apply to the armature thereof during the early part of the movement of that solenoid. During the last portion of the movement of the armature 53, the force applied to that armature will be less than normal; and hence the magnitude of the impact between the armature 53 and the stator 39 will be smaller-than-usual.

The axis of the shaft 56 is disposed adjacent the lower surfaces of the stator laminations 23 and 24. This is important because it enables substantially all portions of the magnetic gaps between the armature 53 and the surfaces 32 and 38 to apply pulling forces to that armature.

The loose engagement between the shaft 56 and the bushings 58 permits the armature 53 to float relative to the plates 26 and 22, and thus relative to the stator 39. That floating action is important; because it permits the bearing surfaces 49 and 51 at the right-hand face of the armature 53 to intimately engage the surfaces 36 and 38 on the laminations 24, whenever that armature is in its right-hand rotated position, while also permitting the bearing surfaces 49 and 51 at the left-hand face of that armature to intimately engage the surfaces 30 and 32 on the laminations 23, whenever that armature is in its lefthand rotated position. The resulting intimate engagements between the bearing surfaces 49 and 51 and either the surfaces 30 and 32 or the surfaces 36 and 38 will minimize chattering and noise.

The pin 64 is located approximately midway between the surfaces 30 and 32, and also is located approximately midway between the surfaces 36 and 38. This is important, because it requires the magnetic flux lines adjacent the bearing surfaces 49 to withstand only about one half of the restorative forces within the springs 62, and it requires the magnetic flux lines adjacent the bearing surfaces 51 to withstand only about one half of the restorative forces within the springs 62. The magnetic forces adjacent the bearing surfaces 49 are easily able to withstand. one half of the restorative forces within the springs 62; and, similarly, the magnetic forces adjacent the bearing surfaces 51 are easily able to withstand one half of the restorative forces within the springs 62. As a result, those magnetic forces are able to minimize chattering and noise.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

1. An electromagnetic device which comprises:

(a) a stationary member that provides a path for magnetic flux lines,

(b) an armature that is mounted for movement relative to said stationary member,

(0) a winding that can develop magnetic flux lines which will flow through said path and through said armature,

((1) said stationary member having a surface that is generally parallel to the path of movement of said armature,

(e) said armature having a surface adjacent one side thereof that is adapted to be disposed in confronting relation with said surface on said stationary member to provide a generally linear magnetic gap,

(f) said surface on said stationary member coacting with said surface on said armature, whenever said armature is in confronting relation with said surface on said stationary member, to subtend a very small acute angle,

(g) said surfaces on said stationary member and on said armature being disposed so the width of said generally linear magnetic gap between said armature and said stationary member is greatest when said armature is spaced away from said stationary member and is least when said armature is close to said stationary member,

(h) the angular displacement of said surface on said stationary member from said surface on said armature helping to provide a generally flat force displacement curve for said electromagnetic device throughout the major portion of the movement of said armature,

(i) said stationary member having a second surface that is generally transverse of said path of movement of said armature and that is spaced wholly away from the first said surface on said stationary member,

(j) said armature having a second surface adjacent said one side thereof that is adapted to be disposed in confronting relation with said second surface on said stationary member to provide an inverse magnetic gap and that is spaced wholly away from the first said surface on said armature,

(k) said second surf-ace on said armature being spaced from said second surface on said stationary member whenever the first said surface on said armature is spaced from the first said surface on said stationary member, and said second surface on said armature being immediately adjacent said second surface on said stationary member whenever the first said surface on said armature is immediately adjacent the first said surface on said stationary member,

(1) said generally linear magnetic gap and said inverse magnetic gap simultaneously responding to energization of said winding to urge said armature to move relative to said stationary member,

(m) part of said second surface on said armature always being immediately adjacent part of said second surface on said stationary member,

(n) whereby said inverse magnetic gap is narrow.

2. An electromagnetic device as claimed in claim 1 wherein said armature rotates, wherein the first said surface on said armature is a rcuate, wherein the first said surface on said stationary member is straight and is roughl tangential to an arc defined by the first said surface on said armature as said armature rotates, and wherein the pivot about which said armature rotates is closely adjacent to said second surface on said armature and is remote from the first said surface on said ar-mature.

3. An electromagetic device as claimed in claim 1 wherein said stationary member has a third surface that coacts with a third surface on said one side of said armature to provide a second inverse magnetic gap, said third surface on said stationary member being adjacent the first said surface on said stationary member and coacting with the first said surface on said stationary member to subtend an obtuse angle that is close to ninety degrees, said third surface on said stationary member and said second surface on said stationary member being substantially co-planar.

4. An electromagnetic device as claimed in claim ll wherein said armature rotates about a pivot and wherein said stationary member has a third surface that coacts with a third surface adjacent said one side of said arm-ature to provide a second inverse magnetic gap, said second surface on said armature being spaced from said third surface on said armature and being adjacent said pivot for said armature.

5. .An electromagnetic device which comprises:

(a) a stationary member that provides a path for magnetic flux lines and also provides a second path for magnetic flux lines,

(b) an armature that can actuate a device and that is mounted for movement relative to said stationary member from an initial position to a moved position and from said initial position to a second moved position,

(c) a winding that can develop magnetic flux lines which will flow through the first said path and through said armature to move said armature from said initial position to the first said moved position, a second winding that can develop magnetic flux lines which will flow through said second path and through said armature to move said armature from said initial position to said second moved position, and

(d) a spring that acts against said stationary member and said armature and that is spaced from said device actuated by said armature by the interpositioning of said armature between it and said device,

(e) whereby said device actuated by said armature will be substantially free from stresses due to said spring,

(f) said spring being under substantial stress at all times, whether said armature is in its initial or its moved position,

(g) said initial position of said armature being located between the first said and said second moved positions of said armature, and

(h) said spring'normally holding said armature in said initial position.

6. An electromagnetic device which comprises:

(a) astator,

(b) an armature that is mounted for movement relative to said stator and is movable from an initial position to either of two moved positions,

(c) a winding that causes magnetic flux lines to flow in said stator and said armature to move said armature from said initial position to one of said moved positions, and a second winding that causes magnetic flux lines to flow in said stator and armature to move said armature from said initial position to the other of said moved positions,

(d) said stator and said armature having surfaces thereon which coact to define a generally linear magnetic gap and having additional surfaces thereon which coact to define a second generally linear magnetic gap,

(e) each of said generally linear magnetic gaps being of inconstant width, and the widths of said generally linear gaps being greatest when said armature is in said initial position and thus is spaced away from said stator and being least when said armature is in either of said moved positions and thus is close to said stator,

(f) said generally linear gaps being at the same end of said armature but being adjacent opposite sides of said armature.

7. An electromagnetic device as claimed in claim 6 wherein further surfaces on said stator and said armature coact to define an inverse magnetic gap, and wherein still further surfaces on said stator and armature coact to define a second inverse magnetic gap, said further surfaces on said stator and armature being remote from the first said surfaces on said stator and said armature, said still further surfaces on said stator and armature being remote from said additional surfaces on said stator and armature, whereby said inverse magnetic gaps are remote from said generally linear magnetic gaps, the first said winding causing magnetic flux lines to flow through the first said generally linear magnetic gap and through the first said inverse magnetic gap Whenever it is energized, said second winding causing magnetic flux lines to flow through said second generally linear magnetic gap and through said second inverse magnetic gap whenever it is energized.

8. An electromagnetic device as claimed in claim 6 wherein said armature is rotatably mounted on a pivot and wherein the first said surfaces and said additional surfaces on said stator and on said armature are remote from said pivot so said gnerally linear magnetic gaps are remote from said pivot, wherein further surfaces'on said stator and said armature coact to define an inverse magnetic gap, and wherein still further surfaces on said stator and armature coact to define a second inverse magnetic gap, said further surfaces and said still further surfaces on said stator and armature being adjacent said pivot so said inverse magnetic gaps are adjacent said pivot.

9. An electromagnetic device as claimed in claim 6 wherein said stator and said armature have further surfaces thereon that coact to define an inverse magnetic gap, and have still further surfaces thereon to define a second inverse magnetic gap, said further surfaces and said still further surfaces on said stator and on said armature being remote from the first said surfaces and said additional surfaces on said stator and said armature, whereby said inverse magnetic gaps are remote from said generally linear magnetic gaps, each of said inverse magnetic gaps being narrow and having one end thereof substantially closed at all times.

10. An electromagnetic device which comprises:

(a) a stator,

(b) an armature that is mounted for movement relative to said stator,

(c) a winding that causes magnetic fiux lines to flow in said stator and said armature to move said armature toward said stator, and

(d) a spring that urges said armature away from said stator,

(e) said armature having bearing surfaces that are spaced apart from each other and that can bear against said stator,

(f) said bearing surfaces projecting laterally outwardly beyond adjacent portions of said armature to constitute the areas of engagement between said armature and said stator.

11. An electromagnetic device as claimed in claim 10 wherein said spring acts upon said armature at a point intermediate said bearing surfaces, whereby the magnetic flux lines at each of said bearing surfaces are required to apply a force less than the force applied to said armature by said spring.

12. An electromagnetic device as claimed in claim 10 wherein said armature is mounted to float relative to said stator, the floating of said armature relative to said stator enabling said bearing surfaces on said armature to intimately engage said stator and thereby minimize chattering and noise.

13. An electromagnetic device which comprises:

(a) a stationary member that provides a path for magnetic flux lines,

(b) a shaft that is loosely mounted relative to said stationary member,

(c) an armature that is mounted on said shaft and is thus loosely mounted relative to said stationary member,

((1) a winding that causes magnetic flux lines to flow in said armature and in said stationary member to cause said armature to move in a given direction relative to said stationary member, and

(e) a spring that acts against said stationary member and said armature to urge said armature to move in the opposite direction relative to said stationary member,

(f) said armature having bearing surfaces thereon that project laterally outwardly beyond adjacent portions of said armature to constitute the portions of said armature which engage said stator.

(g) the loose mounting of said shaft and said armature relative to said stationary member enabling said bearing surfaces to seat solidly against said stationary member.

14. An electromagnetic device which comprises:

(a) a stationary member that provides a path for magnetic flux lines,

(b) a shaft this is loosely mounted relative to said stationary member,

(c) an armature that is mounted on said shaft and is thus loosely mounted relative to said stationary member,

(d) a winding that causes magnetic flux lines to flow in said armature and in said stationary member to cause said armature to move in a given direction relative to said stationary member, and

(e) a spring that acts against said stationary member and said armature to urge said armature to move in the opposite direction relative to said sttationary member,

(f) said armature having bearing surfaces thereon that :project laterally outwardly beyond adjacent portions of said armature to constitute the portions of said armature which engage said stator,

(g) the loose mounting of said shaft and said armature relative to said stationary member enabling said bearing surfaces to seat solidly against said stationary member,

(h) bushings that are interposed between a loop in said spring and said stationary member,

(i) the ends of said spring bearing against a pin carried by said armature, and

(j) said shaft being rotatably held by said bushings,

(k) whereby said armature and said shaft can rotate freely relative to said loop in said spring while said ends of said spring bear against said pin carried by said armature.

References Cited UNITED STATES PATENTS 621,739 3/1899 Baumann 335266 XR 2,563,271 8/1951 Price 335276 3,305,809 2/1967 Ludwig 335-276 XR BERNARD A. GILHEANY, Primary Examiner.

GEORGE HARRIS, Examiner. 

